The combination weigher with multiple compartment weighing receptacles of the present invention is an improvement and simplification of the weighing machine described and claimed in commonly owned U.S. Pat. No. 4,538,693, the specification and drawings of which are incorporated herein by reference.
Recent combination weighers have used a series of bins or hoppers to collect product from a continuous product supply and to convert that product flow into a series of discrete product groups that are each deposited onto a scale and weighed. Preferably, each discrete product group weighs a fraction of the target weight so that a number of them must be combined to obtain the package weight. For instance, if the target weight is 100 grams, the weighing machine might create ten discrete fractional weight groups, each having an arbitrary weight between approximately 10 grams and 30 grams. The machine considers the possible fractional weight combinations available by combining the discrete product groups and it selects the combination providing the preferred weight.
The number of fractional weight groups available on any particular machine cycle is important to machine performance. The larger this number, the greater the possibility of finding a combination exactly equal to the preferred weight.
Many combination weighing machines require one scale for each fractional weight group, for example prior art U.S. Pat. No. 3,939,928 to Murakami or U.S. Pat. No. 4,618,011 to Sashiki. In such weighing machines, all available fractional weight groups are not used on each machine cycle; typically about half these groups remain unused. Therefore, the average number of scales used each machine cycle is only approximately half the existing scales.
The scales are an expensive machine component; thus some attempts have been made to reduce the number of scales without a corresponding reduction in available fractional weight groups. For example, see prior art U.S. Pat. Nos. 4,618,012 to Yamano et al., 4,614,243 to Ikeda, 4,560,015 to Minamida, and 4,538,693 to Klopfenstein et al., all of which utilize storage hoppers. These storage hoppers contain fractional weight groups whose weight was determined on a previous scale cycle but which were not then used, and which are available on a present machine cycle. Consequently the available fractional weight groups are increased without a corresponding increase in number of scales; or, conversely stated, an appropriate number of fractional weight groups may be maintained with fewer scales. These storage hoppers have disadvantages, however; they increase overall machine height, provide additional surfaces for product sticking and/or breakage and present a manufacturing cost.
The present invention provides an appropriate number of available fractional weight groups, but with a smaller number of scales and without storage hoppers.